Can't believe I'm the first to add this one:

I'm going with Zane Donovan from Eureka. He went from a (kinda) scrawny nerdy dude to the Hulk. He's like the Trent Reznor of science. (ETA to give the character some credit since the change allowed for his plot-driven transformation from roguish sidekick to roguish hero, story wise).

My vote is Simon, from Misfits (seasons 1-3).

A favourite. Granted, Donna wasn't originally intended to become the companion of the fourth series, and they changed plans once Tate expressed an interest in reprising the role, but in terms of character development between The Runaway Bride and Partners in Crime, it's an amazing transformation that helps solidify…

... breathed new life indeed ... over and over again.

ZUKO! From having his sole purpose in life be killing the Avatar,

I'm going to have to go with Mickey :

You know Rob, you and I have had our differences in the past and I have tried to move past them. But Rizzo the Rat & Snuffaluffagus I just, I just cant man. Ok I can, First Rizzo the rat, Come on. I am from the south there are whole genre's around making fun of my people and I except it, because we deserve it. Accept…

Moriarty

Dr. Doofenshmirtz needs Perry, and even begs him to "THWART ME!"

I think his one goal in life is to mess with Peter's head regardless of how nonsensical the plan is. Hell I have a theory that the Stacy twins are actually clones of Gwen augmented with his DNA and not the offspring of Gwen and Norman. This makes sense because it makes absolutely no sense why he would do this if only…

#13 The Red Skull. So co-dependent he had his consciousness put into a cloned body of Captain America and used this to bring Cap back from the brink of death.

Well this is awkward...

Don't forget Mark Hamill's eulogy in The Man Who Killed Batman! Classic Paul Dini writing there.

If you want to see Karen Gillan in this trailer, DON'T BLINK.

So I guess this was co-written by Phoebe on Friends?